Those are called scopes. Syntax files (*.tmLanguage) bind them to regular expressions which are parsed by the editor to apply colorscheme colors and styles to the matched strings. They are also used by things like auto completion, snippets and plugins.

In addiction, if you want to know which scope is being applied to a specific part of code, you can use the "show_scope_name" command (default key-bindings is "ctrl+alt+shift+p" in win* but you can find it in default key-binds) that shows all scopes applied for the caret position.hope it helps